Abstract

A mode-evolution-based polarization rotator-splitter built on InP substrate is proposed by combining a mode converter and an adiabatic asymmetric Y-coupler. The mode converter, consisting of a bi-level taper and a width taper, effectively converts the fundamental TM mode into the second order TE mode without changing the polarization of the fundamental TE mode. The following adiabatic asymmetric Y-coupler splits the fundamental and the second order TE modes and also converts the second order TE mode into the fundamental TE mode. A shallow etched structure is proposed for the width taper to enhance the polarization conversion efficiency. The device has a total length of 1350 µm, a polarization extinction ratio over 25 dB and an insertion loss below 0.5 dB both for TE and TM modes, over the wavelength range from 1528 to 1612 nm covering all C + L band. Because the device is designed based on mode evolution principle, it has a large fabrication tolerance. The insertion loss remains below 1 dB and the polarization extinction ratio remains over 17 dB with respect to a width variation of +/− 0.12 µm at the wavelength of 1570 nm, or +/− 0.08 µm over the entire C + L band.

Figures (7)

The schematic top view (a) and cross section views (b)(c)(d)(e) of the proposed mode-evolution-based polarization rotator and splitter consisting of a pre-mode converter, a width taper, and an asymmetric Y coupler integrated with a TE mode polarizer.

Comparison of the mode field distributions with and without gold overlap. Electric field in horizontal direction, Ex, is plotted for TE0 mode; magnetic field in horizontal direction, Hx, is plotted for TM0 mode.

The normalized TE0 mode output power from the upper (diamond) and lower (square) Y-branches and the normalized TM0 mode output power from the lower (triangle) Y-branch as function of wavelength excited by TE0 mode input (a) and TM0 mode input (b).